In recent times, speaking from where I live , when a child is talented in English, but unable to spell, it's usually due to dyslexia. It would be unfair to mark a child down because of that.
In fact, I was asked to change a child's report card because of that, which I did.
However, in fairness to the child, I spoke with his parents who were very much aware of this, and wondered how he got an A. We then had the talk about where she could seek help. I also assured them that we were working with him and he was working hard on all suggestions.
I also taught a girl whose writing you couldn't decipher.
Her parents, both engineers, were beside themselves.
We devised a plan. She is now an engineer too.